04-13-2017 Planning Ccommission Packet

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4 | Page Winter Estates, LLC Winter Estates Site Design and Drainage AMI Project Number 171043 www.amiengineers.com Narrative Winter Estates, LLC is proposing to construct 16 townhomes east of Rice Street in Little Canada, MN. The subject property includes approximately 1.80 acres, of which the entirety outside of the right-of way (1.62 acres) will be disturbed by construction activity. The property boundary and right-of-way is proposed to change per Ramsey County comments. The drainage study area encompasses 1.71 acres of the subject property and consists of those sub-basins delineated within the proposed project area. This results in 0.88 acres of new impervious area generated outside of the proposed right-of-way. The site soils consist primarily of “Urban land-Kingsley” and “Kingsley”. Refer to Appendix E for details regarding site soils including NRCS Web Soils Survey data and Appendix D for the Geotechnical Report prepared by Northern Technologies, LLC. Based on the information collected, the geotechnical engineer recommended using an infiltration rate of 0.06 in/hr for the in-situ soils. For this reason, the site was modeled per the curve numbers associated with of soils in NRCS Hydrologic Soils Group D. Rainfall for the 24-hour storm duration in Little Canada, Minnesota for various rain events is provided in Table 2. Table 2. Rainfall for the 24-hour storm duration in Little Canada, Minnesota Storm Event Rainfall (inches) 2-year 2.40 10-year 4.20 100-year 7.40 SOURCE: Atlas 14-Rain Pre-Construction Conditions Within the study area the existing site has three (3) existing drainage sub basins. A delineation of the drainage basin areas can be seen in Appendix A. The size, time of concentration, and curve number along with calculations for the 2-, 10-, and 100- year storm events for existing runoff can be found in Appendix C. The site currently has 0.1 acres of impervious surfaces from houses, garages and driveways. The site either drains overland to the northeast, overland to the southeast, or into the Rice Street storm sewer system. Post-Construction Conditions The design will utilize curb and gutter, vegetated swales, storm sewer, a dry rate control pond and a sand-iron filtration basin to capture and route runoff.